The present invention relates generally to a method and apparatus for sensing an angular position of a rotating member, and more particularly to a flexible quadrature coil circuit for use in an electric motor to facilitate sensing the angular position of a rotor.
Dynamoelectric machines, such as electric motors, are used in numerous applications, such as air compressors, refrigerators and a wide array of appliances. The ability to manufacture these motors at a low cost and operate them efficiently is an important aspect of their utility.
Electronic commutation permits efficient dynamoelectric machine operation. Electronic commutation controls the rotor by controlling the direction of the electrical current that induces rotor rotation. In order to maintain effective electronic commutation of the motor, it is important to accurately monitor the angular position of the rotor. Rotor position data is generally obtained by strategically placing sensors around the rotor inside the motor housing.
Some electric motor applications use Hall-effect position sensors to detect the angular position of the rotor. Typical Hall-effect position sensors for a single phase motor may require up to five wires, namely two leads for the motor, and three wires for the Hall-effect sensors. Because of its numerous connectors, Hall-effect sensors are difficult to add to a sealed motor system. Additionally, Hall-effect position sensors may be unreliable in some applications.
Quadrature coil sensors provide a low-cost alternative to the Hall-effect sensor for detecting the rotor angular position for commutation. Quadrature coil sensors provide accurate information, and can be added to a sealed motor system using a minimal number of wiring leads and connectors.
The use of quadrature coil windings to detect rotor angular position in electric motors is generally known. For example, U.S. Pat. Nos. 5,796,194 and 5,989,419 disclose the use of a quadrature axis winding for sensorless rotor angular position control of a single phase permanent magnet motor.
U.S. Pat. No. 5,796,194 discloses a quadrature axis winding for generating an output signal representative of rotor angular position. The quadrature axis winding is positioned out of phase from a main winding of the stator and is wound between the center notches of the stator teeth.
U.S. Pat. No. 5,986,419 discloses a quadrature axis winding wound between the center notch of two teeth of the stator. A pre-wound quadrature axis is first wound on a forming tool. The winding includes an insulated enamel wire covered with a plastic jacket. U.S. Pat. Nos. 5,764,194 and 5,986,419 are assigned to assignee of the present invention and are incorporated herein by reference in their entirety.
U.S. Pat. No. 5,313,128 to Robinson et al. discloses a flexible printed circuit including a plurality of electrical paths surrounded by a sheath of pliable MYLAR plastic. The flexible printed circuit is attached to a stator assembly with each winding wire wrapped around three separate poles. U.S. Pat. No. 5,313,128 is also incorporated herein by reference in its entirety.
Industrial standards for insulated lead wires used in electric motor windings require that ground insulation material pass an eighteen-month thermal aging test. Flexible laminated circuit technology, which uses plastic-type insulation material, eliminates the need for lead routing insulation, and complies with such industrial standards.
Accordingly, it is desirable to provide a laminated flexible quadrature coil sensor circuit for detecting the angular position of a rotor that is cost-effective to manufacture and simple to install or retrofit to a motor.
In accordance with one embodiment of the present invention, a flexible quadrature coil circuit is provided for use in an electronically commutated dynamoelectric machine for sensing the angular rotational position of a rotor relative to a stator. The stator has a plurality of stator teeth, with each tooth having an inwardly facing arcuate surface with at least one elongated rib and a channel disposed along a vertical axis of the tooth. The flexible circuit includes a flexible electrically nonconductive substrate with a plurality of slots formed in the substrate. The slots are configured to receive the corresponding elongated ribs so as to releasably secure the substrate to the arcuate surface of the stator tooth. At least one continuous electrical conductor is embedded in the substrate in a serpentine pattern so that the continuous conductor forms a plurality of spaced apart vertical conductor portions disposed between selected slots. The conductor portions are vertically aligned with and are received into the channel of the stator tooth when the flexible substrate is secured to the arcuate surface of selected stator teeth.